The present invention relates to a seat belt pretensioner.
Traditionally a seat belt safety restraint comprises a length of belt webbing connected at both ends to load bearing parts of a vehicle, and arranged to pass across a lap, and also diagonally across a torso, of a vehicle occupant. It is selectively fastened across the vehicle occupant by a buckle mechanism engaging a buckle tongue slidably attached to the webbing.
A retractor is fitted at one end of the webbing. To increase comfort for the vehicle occupant the webbing is allowed to pay out under relatively low loads to enable limited movement of the restrained vehicle occupant, for example to reach in-car entertainment controls or storage compartments. The retractor is biased to keep the webbing relatively taut about the vehicle occupant and a locking element is included to lock the retractor against webbing payout in the event of a crash. For example, an acceleration sensor may activate if the vehicle undergoes rapid acceleration or deceleration indicating a crash.
The retractor usually comprises a rotatable spool onto which the webbing is wound biased by a clock spring.
In recent years, pretensioners have been introduced to rapidly pull a length of webbing to actively tighten the seat belt about the vehicle occupant in the event of a crash condition being sensed. This takes up any slack that may have developed in the belt and helps to more correctly position the vehicle occupant in the seat to maximize the effect of the belt protection and of any secondary safety restraint such as an airbag.
Such known seat belt pretensioners are bulky, costly and comprise many parts. They are single operation devices that cannot operate a second time and may jam the retractor preventing webbing from being either extracted or retracted.
Seat belt pretensioners can be constructed according to the invention which have smaller package sizes and which function as or close to normal even after the pyrotechnic device has fired.
There is provided in accordance with the present invention a seat belt pretensioner comprising: a piston; a tube housing the piston; a force reservoir, activatable when a crash is sensed to drive the piston along the tube; a resilient steel band connected to the piston; and a means for selectively connecting the steel band to a retractor spool.